Stir together first 5 ingredients. Add pepper to taste. Serve immediately, or cover and chill up to 1 week.
Horseradish-Dijon Potato Salad: Cook 6 to 8 medium potatoes (about 3 lb.), cubed, in boiling water to cover in a Dutch oven over medium heat 15 to 18 minutes or until tender. Drain and let cool slightly. Toss with 2/3 cup Horseradish-Dijon Sauce. Serve immediately, or cover and chill until ready to serve. Makes 6 servings. Prep: 10 min., Cook: 18 min.